Effects of Metal Accessibility on Catalytic Performance for Pt/H- Mordenite.

Exposure to water vapor of calcined precursors of 0.5% Pt/H- Mordenite catalysts before reduction induces formation of larger Pt particles after reduction, but also enhances the catalytic activity for methylcyclopentane (MCP) conversion. Adsorption of MCP in the pores of the metal-free zeolite indicates a high extent of pore filling with physisorbed MCP under reaction conditions, favoring transport limitation by single file diffusion. Quantitative analysis by TPO of the coke formed during catalysis shows that most of it is formed on acid sites. This coke swiftly fills the zeolite pores, so that only sites near the external surface are used in the steady state of the catalytic process. The beneficial effect of exposing the calcined catalyst precursor to water is therefore attributed to an enhanced accessibility of the sites during catalysis of MCP.